Radio coverage is a crucial parameter when designing new radio-based communication networks and when managing existing networks. Without adequate (geographical) radio coverage some communication services or other application services may not be available to users of the network at cell borders or so-called coverage holes.
In emerging markets, radio coverage is very important since site acquisition, base station hardware and installation costs could be reduced if fewer base transceiver stations, but with enhanced coverage, could be employed.
In developed markets, existing networks are typically denser and rural coverage may not be a major problem. However, also in such developed networks, in particular in urban environments, there are still coverage holes with no or poor radio coverage. For example, such urban coverage holes may be experienced in indoor environments.
The straightforward approach when improving radio coverage is to boost the downlink output power. However, traditional base transceiver stations are often already run at or near their maximum limits in output power. This means that no or only marginal further coverage increases are possible with this technique.
Improved downlink capacity and also increased radio coverage can be achieved by using transmit diversity. Transmit diversity uses signals that originate from two or more independent sources but that have been modulated with identical information-bearing signals. These signals may therefore vary in their transmission characteristics. Transmit diversity alleviates the negative effects of fast fading in the networks.
Global System for Mobile Communications (GSM) and such systems adopting the Enhanced Data rates for GSM Evolution (EDGE) technology today employ a version of transmit diversity denoted frequency hopping in the art. Frequency hopping is a transparent transmit diversity scheme since no new receiver algorithms are required. Frequency hopping implies hopping between or switching of carrier frequencies during radio transmissions. The transmitted radio signals are subject to multipath propagation, which results in space and frequency dependent multipath fading at the receivers. Since the multipath fading is frequency selective, the fading can be combated by this hopping between carrier frequencies.
Thus, there are techniques in the art for improving the radio coverage for downlink traffic channels by the introduction of frequency hopping. However, frequency hopping is currently not allowed to be used for the broadcast control channel (BCCH). This means that the coverage of a base transceiver station will be limited by the BCCH coverage of that station.
The document US 2003/0072293 discloses a technique for improving the overall spectral efficiency of a wireless telecommunication system. The technique involves transmission of a multiframe signal having a plurality of sub-frames with predefined logical channels repeatedly embedded in predefined sub-frames. A transmitter diversity is applied using antenna and/or polarization hopping sequences such that during the transmission of the multiframe signal, each logical channel is transmitted at least two times with a different antenna and/or polarization.